Nonemitting electrode structure



y 1942. w. G. TAYLOR 2,282,097

NON-EMITTING ELECTRODE STRUCTURE Filed March 29, 1940 Coating of mefa/ of group 8 Carbon/zed l surface (2/7192? Zf/Of Patented May 5, 1942 UNITED STATES PATENT OFFICE NONEMITTING ELECTRODE STRUCTURE Warren G. Taylor, Chicago, Ill.

Application March 29, 1940, Serial No. 326,584

3 Claims.

This invention relates to a non-emitting electrode structure for space discharge devices and more particularly for use in connection with thoriated types of hot cathodes.

In order to obtain certain characteristics in a space discharge device it is frequently necessary to dispose grids and even anodes quite close to cathodes. Since the thoriated type of cathode operates at a high temperature, it is evident that the physical proximity to the cathode of normally non-emitting electrodes will result in heating of these latter electrodes. This is particularly true of grid electrodes.

In addition thereto, electron bombardment will elevate the electrode temperature. Reflection and radiation from an anode or solid plate will also tend to heat grids. The net result is that a so-called cold electrode is in reality an electrode which is normally operating at an elevated temperature.

In the event that any cathode material, that is, thorium or thorium oxide is evaporated or sputtered from the cathode, some may deposit on one or more of the other hot electrodes which should be normally non-emitting. If the material out of which the hot electrode is made is a suitable base for the thorium, then it is obvious that the deposited thorium will result in emission from what should normally be a non-emitting electrode.

The closer a grid electrode is to the cathode, the hotter it is likely to be, the more likely it is to have thorium deposited on it, and the greater the efiect of the emission, since a grid in this position exercises an extremely delicate control.

In order to be satisfactory as a'grid material, a substance should have a high melting point,

low vapor pressure, should surrender substantially all absorbed gases when hot during the evacuation process, should not itself sensibly emit electrons under all operating conditions, and in addition have the usual normal commercial requirements of cheapness and workability. f the metals generally available, iron and nickel would be satisfactory except that they melt and vaporize too easily. Thus, in tubes having carbon or graphite anodes it is necessary to heat the electrode to extremely high temperatures for relatively long times during processing and this usually results in an overheating of the metallic electrodes. Furthermore, during operation many tubes are subjected to extreme overloads where the grid and anode electrodes are operated at a temperature corresponding to red heat or higher.

Under such conditions, iron or nickel would not stand up.

Tungsten as a material for grids is difficult to handle since it is tough and springy. Furthermore, any thorium falling on tungsten will result in emission if the tungsten is hot since tungsten is an excellent base.

Tantalum is ordinarily suitable for grid and anode electrodes. It has one serious drawback however in that its gas absorption characteristics under high temperatures are not always suitable to working conditions.

On an extreme overload some absorbed gases may be released with disastrous results to the tubes. If the tantalum is thoroughly cleaned and free of all gas, it provides a rather excellent base in the event that any thorium falls on it.

Molybdenum is not as easily handled as tantalum and does not absorb gases as readily as tantalum. However, when thorium falls on it, molybdenum is even a better base material than tantalum so that any electrode operating at an elevated temperature will tend to emit.

By the invention herein disclosed it is possible to utilize as a grid or anode material any one of the above three metals without regard to their characteristics of being a satisfactory base material for thorium. Any one of the metals, that is tungsten, tantalum or molybdenum, when treated as described herein retains its normal properties as previously pointed out, when used as a grid or anode with the exception that substantially all tendency for emission of electrons due to thorium falling thereon is suppressed and eliminated so completely that this is no longer a factor in the choice of metal.

In general this invention contemplates the use of tungsten, tantalum or molybdenum as a material for grids and anodes and subjected to the following treatment. A quantity of any one or more of the metals of group 8 'of the periodic table of elements is applied to any one of the three base materials that is tungsten, tantalum or molybdenum. The application may either be in the form of a plated coating or may be melted into the material to form an alloy. The quantity of such additional metal or metals of group 8 may be very small and in practice the added ingredient is generally driven out by heat to the surface of the base material to form a coating.

Thus, for example, a base wire of tantalum, tungsten or molybdenum may be plated with platinum, the coating being extremely minute for the sake of cheapness rather than anything else. Instead of platinum, iridium or osmium may be used. Any one of the three latter elements is particularly desirable for the reason that the melting points are high and vapor pressures are low.

Thus, if a grid must withstand a high tem- 5 metals will withstand extremely high temperal0 tures and will be easily driven oif. However, as long as any one of these metals remains on the surface of the base material, there will be practically no tendency for emission to occur even at an elevated temperature in case any thorium 1o settles on the electrode.

This tendency to non-emission may be due to the fact that the thorium does not remain on the material but is driven off. However, irrespective of how this occurs, I have found that this 2 tendency toward non-emission may be enhanced to an even greater degree by the application of carbon to the treated electrode.

' Thus, as an example, a molybdenum wire which has been suitably cleaned by heating in 2 a hydrogen atmosphere may have a thin plating of latinum thereon. The hydrogen cleaning of the wire may occur after plating if desired. Thereafter this wire may be washed in hot water. The wire may then be made up into the 30 form of a grid or other electrode and then sprayed with a mixture of alcohol and aquadag. Thereafter this electrode may be heated in a hydrogen atmosphere until the surface is shiny and clean. This heating may be done during the 35 final evacuation and Kettering steps. The hydrogen atmosphere is not a necessity since the customary evacuation conditions may create a reducing atmosphere around the wire. A grid or anode electrode treated in this manner will have 40 posing one of the normally non-emitting electrodes.

Referring to the drawing a space discharge device may have an envelope l0 or glass or any other suitable material the interior of which is suitably evacuated. Supported within envelope N as by means of a stem H are a plurality of electrodes consisting of a cathode l2 of the thoriated type adapted to emit when heated. Surrounding cathode l2 is a control grid l3 and beyond the grid is an anode I4. Anode I may be of metal and if desired and as far as this invention is concerned may be handled in the same way as grid IS. The anode may also consist of graphite. In any event, grid l3, as an example of a normally non-emitting electrode which under operating conditions may be hot and upon which thorium may be deposited from cathode I2, is constructed of any one of the metals tantalum, tungsten or molybdenum treated as previously described.

What is claimed is:

l. A space discharge device having a thoriated incandescible cathode and a non-emitting electrode having a core of the group tungsten and molybdenum, said core having as a cover over its entire surface an intimately bound thin surface layer oi. one or more metals or group eight of the periodic table with the outer surface of.

said layer carbonized.

2. A space discharge device having a thoriated incandescible cathode and a non-emitting electrode having a core of the group tungsten and molybdenum, said core having as a cover over its entire surface an intimately bound thin surface layer of one or more metals of group eight of the periodic table having a melting point of the order of platinum and having the outer surface of said layer carbonized.

3. A space discharge device having a thoriated incandescible cathode and a non-emitting electrode having a core of the group tungsten and molybdenum, said core having as a cover over its entire surface an intimately bound thin surface layer of platinum with the outer surface carbonized.

WARREN. G. TAYLOR. 

